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Full text of "Text Book Of Mechanical Engineering"

Appendix II.

791

rises against the trolley c supporting the ingot mould R ; and the
load is resisted by the head F, being transmitted thereto by the
fixed plunger E. The head F is supported by rods PP attached
to the lifting plungers NN, and its upward movement is prevented
by the nuts GG, while through it there pass two rapid-pitched
screws MM, upon each of which is a wheel L gearing with the
nuts GG; and lastly there is a small hydraulic cylinder j, whose
piston moves a rack in gear with the wheel K, which again forms
a nut on the screw M. Supposing it be required to raise F to
admit the mould, the piston j is moved so as to turn K, and with
it M, thus releasing nuts GG, and moving them upward to a very
small amount. Then piston j is locked in the new position.
Next, the rams NN are raised, lifting F and also the screws MM
through wheel K, which is npw a fixed nut. MM thus revolving,
the nuts GG are moved upward at "the same rate as F. When the
proper height has been reached, the plunger j is moved back to
its original position, bringing nuts GG on to their seats to receive
the upward thrust.

The ingot mould consists of iron rings s s, in two concentric
sets, within which are placed blocks of firebrick TT, and a lining
of ganister. At each end, ring plates uu are fixed, to hold the
bricks in place, and the open mould is covered with loose pistons
Q Q, again protected by fireclay slabs. When compression occurs,,
the plunger enters the mould by the rising of the latter, and the
gases that escape through thie bricks pass upward or downward,
finally leaving by the holes in plates uu. A very high intensity
of pressure is absolutely necessary, less than 15 or 20 tons per
square inch being very doubtful policy. The press shewn can
exert a total pressure of 10,000 tons. (See third preface.)

P. 82. The Basic Steel process, known also'.as the
* Bessemer-Basic/ was introduced by Thomas and Gilchrist in
1886 for producing steel from phosphoric pig, which had pre-
viously proved useless for steel making. Its success is due to a
magnesia lining to the converter, obtained by crushing dolomite
or magnesium limestone that has been previously dried, mixing it
with tar, ramming it as a lining, and heating to 'coke' the tar.
When this 'basic' lining has been heated, 14 to 20 % of the
charge weight is thrown in as burnt lirne, after which the pig is